1. Technical Field
The invention relates to vibration dampers and in particular to a damper for use in a vehicle and specifically to a damper for mounting in the vehicle seat to isolate resident frequencies imparted on the passenger's seats. Even more particularly the invention relates to such a vibration damper having an anti-rotational device to prevent excessive rotation of the damping mass due to non-translational vehicle inputs.
2. Background Information
Damping devices and in particular dynamic dampers, are currently used in many applications and in particular in the automobile industry for damping out various vibrations imparted on portions of the vehicle caused by the engine, tires and road conditions. One problem that exists is that vibrations which result from resonance frequencies are imparted on the passenger seats of minivans which eventually could cause discomfort to the passenger.
Various types of dampers have been used to dampen out unwanted vibrations on various structures. These are generally of the shear type dampers in which a mass is attached in some fashion to an elastomeric member wherein the elastomeric material is bonded directly to the mass with the elastomer acting in shear. These dampers are then attached in some fashion to the structure or vehicle for damping out the unwanted frequencies.
Other types of dampers use a bushing arrangement wherein an elastomer is bonded between inner and outer cylindrical members such as shown in U.S. Pat. No. 5,769,380 and 4,889,328. Various other dampers using an elastomer and a damping mass are shown in U.S. Pat. Nos. 4,580,666; 4,800,306; 3,419,111; 5,876,023; 5,876,024 and 5,799,930.
However, a problem that occurs in such dampers is that the dampers are prone to exhibit very erratic motion both translational and rotational caused by excessive rotation due to non-translational vehicle inputs.
None of these prior art dampers, especially those that have a suspended mass, have any type of anti-rotational device to limit the angular swing of the mass which reduces the effectiveness desired to be achieved thereby. Likewise, many of the prior art damping devices, especially those intended for use in a vehicle seat, are difficult to manufacture in an economical manner and in a size and weight acceptable for use in the automotive industry.
Therefore, the need exists for an improved vibration damper intended primarily for use in a vehicle seat, which is relatively easy and inexpensive to manufacture and which may include an anti-rotational device to avoid erratic motion of the damper.